Do Plants Get Stressed Out?

A plant can begin conserving water, adjusting its metabolism or activating defence before its leaves show visible damage. These responses help it cope with difficult conditions, but growth may already be slowing. To understand what is happening, distinguish the condition affecting the plant from its response and any damage that develops.

Different stressors create different problems

Abiotic stress comes from non-living conditions such as drought, flooding, heat, cold, unsuitable light, salinity, nutrient imbalance, mechanical injury or harmful chemicals. Their effects can be quite different. Dry roots struggle to supply water, whereas waterlogged roots may be short of oxygen. Excess salts can make water harder to acquire even when the substrate is wet. The electrical conductivity (EC) of a root-zone sample helps assess dissolved ions, although it cannot identify which ions are present or establish the cause of damage on its own.

Biotic stress involves organisms or biological agents that adversely affect the plant. Fungal pathogens, viruses, insects and plant-parasitic nematodes challenge different tissues in different ways; competition from neighbouring plants can also limit access to resources. A microorganism's presence is not necessarily a problem, however. Many root-associated microbes are harmless or beneficial, and an insect feeding on a leaf does not produce the same physiological demands as a root infection.

A response can start before injury appears

When water becomes scarce, stomata may close to limit water loss, changing carbon dioxide uptake and photosynthesis. Other challenges trigger shifts in hormone signalling, gene expression, antioxidant activity and growth. Plant cells also produce reactive oxygen species (ROS), which participate in signalling at controlled concentrations but can contribute to injury when their production overwhelms protective systems. Dietz and Vogelsang (2024) propose that the interaction between stress-specific sensors and redox signalling helps plants adjust the strength of their responses.

Protective changes are not always visible. A cannabis grower may notice that a pot has become unusually light while the leaves still look firm. The plant may already be reducing stomatal opening to conserve water, limiting CO₂ uptake and photosynthesis before any obvious wilting appears.

A crop may maintain turgor while growing more slowly, and a damaged leaf may stay discoloured after the original problem has been corrected. Du et al. (2024) describe how defence and repair involve resources that would otherwise be available for growth and reproduction, although the extent of that trade-off varies with the response and the growing conditions. For the mechanisms linking local events with wider plant responses, see Plant Signalling: How a Local Attack Triggers a Wider Response.

How plants adjust: acclimation, avoidance and tolerance

A plant may acclimate to a changed environment during its lifetime. Under limited water availability, for example, it can alter stomatal regulation, root growth and the balance of compounds that help cells retain water. Changes in membrane properties, protective enzymes and growth allocation are other possible adjustments. Acclimation can help maintain function under difficult conditions without making those conditions desirable for crop production.

Two related strategies describe different aspects of coping. Avoidance reduces exposure to the challenge: roots reaching a moister part of the substrate may help prevent dehydration. Tolerance allows tissues to function despite exposure, as when cells regulate ion concentrations under salinity. These mechanisms can operate together, and plants differ in their capacity to use them according to genotype, developmental stage and previous conditions.

When Stresses Collide

A plant facing heat, drought or disease may have to deal with several challenges at once. Their effects do not simply add up. Pandey et al. (2024) reviewed experiments in which drought, temperature or salinity changed a plant's susceptibility to pathogens. In some cases, drought-induced stomatal closure reduced opportunities for pathogens to enter through leaf pores. Other combinations increased damage. The sequence and severity of the stresses also influenced the outcome.

For a cannabis grower, consider a plant wilting on a hot afternoon while its substrate is still wet. High evaporative demand may be increasing water loss, while poorly aerated or damaged roots struggle to replace that water. Adding more water could worsen an existing oxygen shortage. Checking substrate moisture, drainage and root health alongside temperature provides a better starting point than treating every wilted plant as thirsty.

The research also shows why deliberately adding stress is not a reliable way to improve plant resistance. A treatment that reduces one disease under particular experimental conditions may still compromise growth or create other problems.

Priming and stress memory

An earlier exposure can change how a plant responds to a later challenge. This is called priming: the plant may respond faster or more effectively without keeping its defences continuously active. The later challenge can also differ from the first. Aswathi et al. (2025) and Sanchez-Lucas (2026) review how changes in signalling and gene regulation contribute to these responses.

Arıkan et al. (2026) tested salt priming in young Arabidopsis plants, comparing previously exposed plants with unprimed controls during a later salt treatment. Their experiment examined both the plant response and associated changes in gene expression and chromatin, the material in which DNA is packaged.

Changes that persist after an exposure and influence a later response are described as stress memory. They need not involve a permanent genetic change, and an effect within one plant does not establish inheritance by its offspring. For growers, the useful point is that plants with different environmental histories may respond differently to the same conditions.

That history can also complicate experiments. Vannay et al. (2026) explain that plants kept smaller by an initial dry period may use less water during a second one. They can then appear more drought-resistant simply because they experience a different degree of water shortage. Comparing their performance requires accounting for plant size and water use.

Does mild stress make a plant stronger?

Can a little stress increase THC in cannabis? The idea is popular among growers, and it connects to a biological phenomenon called hormesis. In some experiments, mild stress stimulates a measurable plant response, while stronger stress suppresses it. Erofeeva (2024) discusses possible physiological explanations, including changes in how plants allocate energy between growth and defence. Whether this translates into increased THC concentration is a separate question that requires cannabis-specific evidence.

The outcome being measured matters. Increased antioxidant activity is not the same as faster growth or a larger harvest. A smaller crop can also contain a higher concentration of a compound while producing less of it in total.

For cannabis growers considering stress treatments to influence cannabinoids or terpenes, the relevant question is what cannabis experiments actually measured. That evidence is discussed separately in Does Stress Increase THC or Terpenes?

What growers should investigate first

Begin with what changed before the problem appeared. An altered irrigation schedule, a hotter afternoon or a gradual fall in water use can help narrow the investigation. Check those changes against root-zone conditions and signs of pests or disease rather than treating “stress” as a diagnosis.

Measurements need to represent the conditions being investigated. The pH and EC of freshly mixed feed, for example, do not necessarily describe the solution around the roots. Follow the plant’s development as well: damaged leaves may remain discoloured after the cause has been corrected, so their appearance alone cannot show whether the problem is continuing.

Before You Add Anything, Learn to Read the Plant develops this approach, starting with the growing environment and root zone before interpreting leaf symptoms or adding treatments.

References

Aswathi, K. P. R., Ul-Allah, S., Puthur, J. T., Siddique, K. H. M., Frei, M., & Farooq, M. (2025). The Plant Mind: Unraveling Abiotic Stress Priming, Memory, and Adaptation. Physiologia Plantarum, 177(4), e70372. DOI: 10.1111/ppl.70372.

Dietz, K.-J., & Vogelsang, L. (2024). A general concept of quantitative abiotic stress sensing. Trends in Plant Science, 29(3), 319–328. DOI: 10.1016/j.tplants.2023.07.006.

Du, B., Haensch, R., Alfarraj, S., & Rennenberg, H. (2024). Strategies of plants to overcome abiotic and biotic stresses. Biological Reviews, 99(4), 1524–1536. DOI: 10.1111/brv.13079.

Erofeeva, E. A. (2024). Plant hormesis: The energy aspect of low and high-dose stresses. Plant Stress, 14, 100628. DOI: 10.1016/j.stress.2024.100628.

Pandey, P., Patil, M., Priya, P., & Senthil-Kumar, M. (2024). When two negatives make a positive: the favorable impact of the combination of abiotic stress and pathogen infection on plants. Journal of Experimental Botany, 75(3), 674–688. DOI: 10.1093/jxb/erad413.

Sanchez-Lucas, R. (2026). Plant defence priming and memory mechanisms under climate change. Essays in Biochemistry, 70(1), 5–14. DOI: 10.1042/EBC20250050.

Arıkan, B., Çakır, Ö., & Turgut Kara, N. (2026). Epigenetic and transcriptomic features of stress memory during salt-stress priming in arabidopsis. Plant Science, 362, 112775. DOI: 10.1016/j.plantsci.2025.112775.

Vannay, G. J., Otegui, M. E., Capella, M., & Chan, R. L. (2026). Rethinking drought memory in crops: A call for improved experimental design. Plant Science, 364, 112929. DOI: 10.1016/j.plantsci.2025.112929.